The present invention relates to a novel positive-working photoresist composition or, more particularly, to a chemical sensitization-type positive-working photoresist composition in the form of a solution capable of giving a finely discrete patterned resist layer having an excellent cross sectional profile with high sensitivity to actinic rays and high pattern resolution.
As is known, the photolithographic patterning process by utilizing a positive-working photoresist composition is widely practiced in the manufacture of various kinds of semiconductor devices such as ICs, LSIs and the like. The photolithographic patterning work using a positive-working photoresist composition is performed by first forming a layer of the photoresist composition on the surface of a substrate such as a semiconductor silicon wafer and the photoresist layer is exposed to actinic rays such as ultraviolet light patternwise through a photomask bearing a desired device pattern to form a latent image of the pattern, which is then developed by dissolving away the resist layer in the ultraviolet-exposed areas with a developer solution leaving a patterned resist layer to serve as a protective resist in the subsequent treatment of the substrate surface such as etching. Positive-working photoresist compositions used in the above described photolithographic patterning typically-have a formulation comprising an alkali-soluble novolac resin as a film-forming agent and a quinone diazide group-containing compound as a photosensitive ingredient uniformly dissolved in an organic solvent.
Along with the trend in the semiconductor technology toward a high degree of integration in the semiconductor devices increasing year by year, the manufacturing process of VLSIs and the like requires an extremely high fineness of the photolithographic patterning works sometimes in the ranges of the sub-micron order or quater-micron order. This requirement for the high fineness of patterning to be accomplished naturally depends on the performance of the photoresist composition and also on the effective wavelength of the actinic rays, e.g., ultraviolet light. For example, the wavelength range of the ultraviolet light used in the photolithographic patterning work is under a trend of decreasing from the g-line and i-line to deep-ultraviolet light and excimer laser beams such as KrF laser beams as an important light source in this technology.
Chemical sensitization-type photoresist compositions as a class of the photoresist compositions are now under active development works because an ultraviolet light of a shorter wavelength such as deep ultraviolet and excimer laser beams can-be utilized for the patternwise exposure than for the conventional photoresist compositions of the above mentioned type comprising a novolac resin and a quinone diazide group-containing compound so as to provide a possibility of obtaining a high resolution and a high sensitivity by virtue of the catalytic reaction and chain reaction of a quantum yield larger than 1 by the acid generated by the irradiation with actinic rays,
Since the chemical sensitization-type photoresist composition has been developed with an object to comply with the requirement for an extremely fine patterning of a width of 0.3 .mu.m or even finer, an attention is recently directed to the cross sectional profile of discrete or isolated resist patterns. For example, it is sometimes the case that, when a patterned resist layer has a cross sectional profile standing on the substrate surface with a downwardly decreasing width toward the substrate surface, the patterned resist layer eventually falls down on the substrate surface. This phenomenon is a very serious problem to be solved when a chemical sensitization-type photoresist composition is to be used for the photolithographic patterning of extreme fineness.